1. Field of the Invention
The present invention relates to a diversity antenna apparatus and a diversity antenna control method for selecting a desirable antenna from among a plurality of antennas to receive a radio signal. Particularly, the present invention relates to a multiple elements antenna diversity technique in the channel condition which varies slowly.
2. Related Art
In a frame reception processing according to a conventional wireless local area network (LAN) communication system (for example, in IEEE802.11), a length of a preamble added in front of data is set by assuming a diversity of two elements (IEEE 802.11a, for example).
However, according to a conventional practice, when the number of diversity branches is set to N (N is an integer equal to or larger than 3), one branch is selected from among the N branches during a period of preamble that assumes two branches. Consequently, it is impossible to select a suitable branch, thereby degrading reception characteristic.
With increase of the number of branches, a period of preamble required for selecting a branch becomes long. Therefore, a period of preamble to be used for other processing such as synchronous processing becomes short, degrading the reception characteristic.